Hair loss is a common problem faced by both men and women. It is perfectly normal to shed between 50 and 100 hairs from the head every day, according to the American Academy of Dermatology Association. However, excessive hair loss that causes progressive thinning of the hair, bald patches, or even total hair loss can be very distressing. There are several possible causes of hair loss, including major stressors, medications, illnesses, autoimmune disorders, tight hairstyles, and genetics.

The biology of hair growth is complex, and in recent years scientists have made strides toward understanding how the various factors listed above cause hair loss. Hair growth occurs within hair follicles, which are tube-like skin pores that enclose the shaft and root of the hair. Most healthy adults have around 80,000-120,000 hairs on their scalps. Each hair follicle repeatedly undergoes a growth cycle that comprises three distinct phases: anagen, catagen, and telogen.

During anagen, which lasts between 2 and 7 years, the hair within the follicle grows about 1 centimeter per month. The follicle then enters catagen, a 2-week transitional phase during which the hair detaches from the blood supply. During the final, inactive stage, or telogen, the follicle sheds the hair. It can then take up to 4 months before the follicle starts to grow a new one.

Two to 3 months after a person experiences a traumatic or stressful event, they can develop telogen effluvium – a type of hair loss in which the follicles remain stuck in the inactive, hair-shedding stage. In March 2021, scientists revealed how chronic stress can keep hair follicles in this inactive state for longer.

The hair follicle is one of the few tissues in the body that can regenerate itself, thanks to special cells known as adult stem cells. Researchers at the Harvard Department of Stem Cell and Regenerative Biology in Cambridge, MA, discovered how chronic stress in mice suppresses the activity of these cells. They showed that a stress hormone called corticosterone, which is the mouse equivalent of cortisol in humans, keeps the follicle stem cells inactive. They found that in the absence of circulating corticosterone, the stem cells underwent many more rounds of regeneration during the animals’ lifetime.

By contrast, high levels of the hormone, as a result of chronic stress, kept them inactive for longer and led to fewer rounds of regeneration. Rather than directly affecting the stem cells, however, corticosterone acted on a cluster of cells under the follicle, known as the dermal papilla. The researchers showed that in mice, the stress hormone prevented the dermal papilla from producing a molecular signal called Gas6, which normally activates the follicle stem cells.

The discovery of how chronic stress affects hair growth could lead to the development of new treatments for hair loss. Currently, there are several treatments available, including medications like minoxidil and finasteride, hair transplant surgery, and low-level laser therapy. However, these treatments may not be effective for everyone, and they can be expensive and time-consuming.

Preventing hair loss in the first place may be the best option. While genetics play a significant role in pattern baldness, other factors like stress and diet can also contribute to hair loss. Eating a healthy diet rich in protein, iron, zinc, and biotin can help promote hair growth. Additionally, managing stress through techniques like meditation and exercise may also help prevent hair loss.

In conclusion, hair loss is a common problem that can be caused by several factors. Understanding the biology of hair growth and the various causes of hair loss can lead to the development of new treatments. Additionally, taking steps to prevent hair loss through diet and stress management